The present invention relates in general to sewing machines and in particular to a new and useful thread monitor for a sewing machine with a lockstitch rotary hook for monitoring the supply of thread in the bobbin of the rotary hook.
Such a sewing machine is known from U.S. Pat. No. 3,845,320. The bobbin used in this arrangement comprises a separating wall provided next to its one flange, for separating a part of the bobbin as reserve area for a certain initial quantity of thread. The separating wall reduces the capacity of the bobbin. Also, the bobbin cannot be filled in the normal manner, but instead, first the reserve area must be filled if the arrangement is to work in the intended manner. In addition, the scanning of the thread supply occurs at a considerable distance from the hub of the bobbin.